Click the thumbnail photos to enhance!
Debelius, Helmut: Schneckenführer Indopazifik / Helmut Debelius.- Hamburg: Jahr 1997
Jahre Verlag GmbH &Co., ISBN3-86 132-203-X
At page 49 are 2 pictures of this species showing the perfect camouflage.
The specimen #2 was identified by Ron Silver at the facebook group ID Please (Marine Creature Identification), thanks!
Species of the family Ovulidae Fleming, 1822 are sometimes mistaken for seaslugs, especially when the shell is covered by the large colourful mantle. Let me quote Bill Rudman:
"One easy way to separate snails from slugs is to look for their eyes. If they are raised from the skin like this then they are a snail. If the eyes are embedded in the skin they are an opisthobranch."
How to cite:
Köhler, E. (2018), published 26 April 2018, Prosimnia semperi (Weinkauff, 1881)
available from https://www.Philippine-Sea-Slugs.com/Look-alike/Ovulidae/Prosimnia_semperi/Prosimnia_semperi.htm